Communication networks are constructed using network models and transfer protocols as guides. Network models and transfer protocols have proliferated over the past few years as new networks have been developed (and existing networks have evolved) to accommodate new end-user, device and application requirements.
The proliferation of network models has focused on monolithic, highly integrated network and network component architectures. Data services (e.g. functionality and products) developed for a network that supports a target group of end-users, devices or applications are usually available only within the geographical reach of that network, and are not easily extendible to another network without extensive modification or complete re-creation. Adding new functionality to installed networks requires complex modifications or overlays to the existing functionality. Conversely, new networks cannot capitalize on functionality and protocols developed for legacy networks, because monolithic integrated designs do not permit porting without complex protocol conversion interfaces. The time required to implement such modifications is incompatible with the modern competitive communications business environment, where the time to market can significantly influence market share. At the same time, the costs associated with installing new network equipment can pose a significant impediment to the deployment of modern network services. For example, many firms (typically those with multiple branch locations) have deployed enterprise networks linking their various branches via lines leased from a network service provider. Legacy enterprise networks of this type were commonly constructed based on any of the X.25, Frame Relay (FR), or Integrated Services Digital Network (ISDN) protocols, and usually involved substantial investment in networking equipment. This investment may make the firm reluctant to incur the cost of new equipment required to utilize modern broadband packet network architectures (e.g. ATM or XGb Ethernet or Internet Protocol [IP]), in spite of the various advantages offered by the newer architecture to the firm and/or the network service provider.
As a result, the present communications network space is a patchwork of modern and legacy networks, each operating under respective network models and transfer protocols (e.g. Ethernet, Time Division Multiple Access (TDMA), frame relay (FR), synchronous transfer mode (STM), asynchronous transfer mode (ATM), X.25, SNA, Video, Transfer Control Protocol/Internet Protocol (TCP/IP) etc.); utilizing different transport media (e.g. copper, fiber, wireless etc.); and frequently owned by different business entities. Networks may be edge-connected by means of gateway interfaces, permitting transport of data between the networks. However, where such networks are dissimilar, adaptation is required to facilitate the transport of data across the networks. In the context of the present invention, adjoining networks are considered to be “dissimilar” or “heterogeneous” if their respective network models, transfer protocols and/or media are sufficiently different that data streams originating in one network cannot be transported by an adjoining network without conversion or reformatting. Such conversion, referred to herein as “adaptation”, is an automated process to enable the transfer of data across the heterogeneous networks.
For example, a firm may operate a legacy enterprise network comprising a site network at each of its various branch locations, and utilizing frame relay for inter-site communications over leased lines provided by a network service provider. The network service provider may wish to extend the frame relay service through an ATM backbone network, in order to take advantage of the superior data transport capabilities of the ATM backbone. Such service extension requires adaptation of data at gateways between the ATM network and each of the involved site networks. Thus data originating in each site network (and conforming to the FR protocol) must be adapted to conform to the ATM protocol before it can be transported across the ATM backbone. Similarly, data arriving at a site network through the ATM backbone must be adapted to conform to the FR protocol before the data is delivered to the site network.
Adaptation to facilitate data service extension scenarios of this type is typically performed in gateway servers provided for that purpose, usually as part of a data services solution specifically engineered to the requirements of the customer. Both of these factors tend to increase costs and reduce flexibility, thereby creating an impediment to their widespread deployment.
Applicants co-pending U.S. patent application Ser. No. 09/158,855, entitled TRANSIT TRUNK SUBNETWORK, which was filed on Sep. 23, 1998, teaches a method of inter-office trunking of PCM signals through an ATM backbone. A PCM data stream received at an ingress gateway is packed into ATM cells having a predetermined length. The ATM cells are transported through the ATM backbone, e.g. over a switched virtual circuit (SVC), to an egress gateway. The egress gateway extracts the data from the ATM cells to recover the original PCM signal.
ATM SVCs are particularly adapted for trunking circuit-switched data streams, because ATM guarantees delivery of each cell, and ensures that cell-ordering is maintained. Thus ATM can readily satisfy the QoS requirements of connection-oriented traffic without excess overhead. However, in some cases it may be desirable to provide trunking through other packet-based networks (such as IP, Ethernet or wireless), in which QoS guarantees may not necessarily be provided. Additionally, the efficiency of utilization of resources within a data packet network used to transport circuit-switched data can also be comparatively low. In particular, trunking facilities are normally provisioned for peak utilization periods. This means that at any given time, some, or possibly most of the channels within a circuit-switched trunk may be idle. However, in order to facilitate recovery of the circuit-switched signals at an egress gateway, the entire trunk signal, including the idle channels, must be transported across the packet data network. This means that at least some of the packets (e.g. ATM cells, IP packets or Ethernet frames) carry null data.
U.S. Pat. No. 5,936,965, which issued to Doshi et al. on Aug. 10, 1999 teaches a system for supporting the transmission of multiple application-layer protocols through a single link using a single byte-stream. The multiple application-layer protocol types supported include asynchronous transfer mode (ATM) protocol data units (PDUs), synchronous transfer mode (STM) PDUs, and variable length (VL) PDUs, as well as subtypes included within these protocol types. Application-layer PDUs are processed at three intermediate protocol layers where the application layer PDUs are prepared, segmented, and repacked as asynchronous block multiplexing (ABM) PDUs. ABM PDUs include a type identification field. Cyclical redundancy checks and other error detection/correction techniques are optionally supported. ABM PDUs are multiplexed within a multiple protocol byte-stream. Multiple protocol byte-stream support is provided through a single link between a transmitter and receiver using a plurality of media, including coaxial cable, wireless, optical fiber, hybrid fiber/coax, satellite, and twisted pair.
Thus the system taught by Doshi et al. is designed to operate in modern networks constructed using a data packet model and a layered architecture. Furthermore, Doshi et al. propose a proprietary ABM PDU format that is not supported by current network standards. Accordingly, the system of Doshi et al. can only operate on proprietary PHY-layer equipment, and thus is incapable of transporting data using the existing network infrastructure. Finally, Doshi et al. do not address the problem of adapting multiple legacy circuit-switched data streams for transport through a data packet network.
Accordingly, a method and apparatus that enables the protocol-independent extension of data services through a broadband packet network with efficient utilization of packet network resources, remains highly desirable.